Control knob



FIG. 1 is a front view of a control knob showing my new design;

FIG. 2 is a bottom plan view thereof; the left side view being identicalthereto;

FIG. 3 is a rear view thereof;

FIG. 4 is a top plan view thereof; and,

FIG. 5 is a right side view thereof.

The ornamental design for a control knob, as shown and described.